[ ] grep -H -n *.c 'TODO:'
[ ] rewrite xml.{c,h}
[ ] check truncation (strlcpy, snprintf etc), especially for paths.
[x] fix timezone in slashdot.xml
    [x] string_append: make sure some fields can only be set once (first field counts?).
    [ ] test new parsetime and gettimetz code.
[ ] xml: check read errors:
	ferror, return code of fread, fwrite, fclose...
[ ] separate codepointtoutf8 and entity handling from sfeed.c into xml.c?
[ ] test again on:
	- Linux (glibc+gcc, musl-gcc, clang, tcc).
	- OpenBSD
	- Windows (cygwin gcc, mingw).
[ ] test shellscripts with ubase/sbase tools.
	[ ] sfeed_update
	[ ] sfeed_opml_export
[ ] feeds file: empty tab (encoding can't be detected?)
[ ] optimize
	[ ] benchmark / profile callstack.
	[ ] gettag() lookup.
	[ ] namedentitytostr lookup.
	[ ] xml parser, etc.
[?] add sfeed_atom ? to aggregate feeds?